1. Field of the Invention
The present invention relates to a liquid ejection apparatus such as an ink-jet recording apparatus for ejecting a liquid such as ink ejecting from a head thereof on a medium (herein after, referred to “recording medium”).
Here, the liquid ejection apparatus is not limited to a printer, a copying machine, a facsimile, etc., using a recoding head for recording on a recording medium by ink ejecting from the head. The liquid ejection apparatus includes an apparatus for ejecting a fluid which may be used instead of the ink from a fluid ejection head corresponding to the recording head on a recording medium corresponding to the recording medium.
The fluid ejection head includes a colorant ejection head used for manufacturing a color filter of a liquid crystal display, an electrode material (conductive paste) ejection head used for forming electrodes of an organic EL display, a field emission display (FED), etc., and a bio-organic substance ejection head used for manufacturing a bio chip, a sample material ejection head such as a precision pipette, etc., in addition to the recording head.
2. Description of the Related Art
There is an ink-jet printer (herein after, referred to “printer”) as an example of the liquid ejection apparatus or the recording apparatus. The printer is provided with a guiding member (which may be called “platen”) at a position opposite to the recording head for ejecting ink drops to a printing paper which is an example of the recording medium or the recording medium, wherein the guiding member predetermines a distance between the printing paper and the recording head. The guiding member extends in the main scanning direction of the recording head and predetermines the distance between the printing paper and the recording head by supporting the printing paper from the underside.
A transfer (paper transfer) roller for transferring the printing paper to the side of the recording head is provided upstream of the guiding member and a discharge (paper discharge) roller for discharging the recorded printing paper is provided downstream of the guiding member. The transfer roller includes a driving transfer roller which is formed by a shaft extending in the width direction of the printing paper and drives rotation and a driven transfer roller which is adjacent to and rotates following the driving transfer roller. Moreover, the discharge roller includes: a driving discharge roller which is localized on a rotation axis extending in the width direction of the printing paper and drives rotation; and a driven discharge roller which is adjacent to and rotates following the driving discharge roller. The driven discharge roller is provided so that it is localized on a driven discharge roller supporting frame of a shape extending in the direction of the main scanning direction of the recording head in the direction of the main scanning direction.
Japanese Patent Application Laid Open No. 2002-19204 discloses a paper transfer apparatus of a recording apparatus in which a vertex of a platen is lower than a line connecting a nip point of a paper transfer roller and a nip point of a paper discharge roller and the paper transfer speed of the paper transfer roller is the same as the paper discharge speed of the paper discharge roller and which performs printing with a good quality even after the end of a paper gets out of the paper transferring roller.
Japanese Patent Application Laid Open No. 2002-248819 discloses restricting the position of a platen in the direction opposite to a recording head of the platen by the planet's colliding with a restricting means by an energizing force of an energizing means and consequently determining a platen gap.
Japanese Patent Application Laid Open No. 1998-211748 discloses moving a gap regulating unit on a shaft of a paper discharge roller driven by a paper transfer motor to the side of engaging with a middle gear by shifting to a platen gap switching position of a carriage, engaging one side of a planet gear with the middle gear according to a rotational direction of the paper transfer motor, rotating a pair of guide rods in the same directions and by the same amounts through a sector gear according to the rotational direction, and shifting a carriage parallel to a printing reference plane.
Each of Japanese Patent Application Laid Open Nos. 2002-19204 and 1998-211748 discloses an apparatus having a function of switching the height of a recording head in order to prevent the rear end of a paper from floating, which makes the configuration of the apparatus complicated because the apparatus should include means for moving a carriage mechanism in the vertical direction. Moreover, Japanese Patent Application Laid Open No. 2002-248819 discloses an apparatus having function of translating a platen in the vertical direction in order to prevent a recording medium for contacting with a recording head, and a constitution performing the function is also complicated.
The elements such as the guiding member, the driving transfer roller, the driving discharge roller, and the driven discharge roller supporting frame described above are installed on a frame material forming the body of the printer like a sub-frame disclosed in Japanese Patent Application Laid Open No. 2002-347304.
However, in case the plurality of elements are installed on one frame material, the elements need to be installed sequentially which is not effective.
Moreover, the frame material is generally made of metal in order to acquire strength and the guiding member is sometimes made of resin because of complexity of its shape and construction. In this case, due to the difference in the rate of thermal expansion between the both, a shear stress is generated in the guiding member and thus the guiding member is deformed. In this case, there is a problem that the distance between the printing paper and the recording head (which may be called “platen gap”) is not uniform and thus quality of recording gets worse. These kinds of problems may be caused by low initial precision of components in addition to the temperature variation. Furthermore, if the driven discharge roller supporting frame is fixed to the frame material by a screw, warpage is generated due to the size change as time goes by and thus a shear stress is generated in the driven discharge roller supporting frame. Thus, similarly with the guiding member, there is a problem that the driven discharge roller supporting frame may also be deformed. If the driven discharge roller supporting frame is deformed, the position of the driven discharge roller is varied. By this, the driven discharge roller contacts the printing paper strongly and there is a problem that contact traces are formed on the printing surface.